The principal phospholipid in the pulmonary surfactant is disaturated phosphatidylcholine (DSPC). Current information indicates that the site of DSPC synthesis is the type II alveolar epithelial cell and that the site of functional activity is the alveolar surface. However, little is known about the mechanisms and control of the transfer of the DSPC from its site of synthesis to its functionally active site. We propose to investigate the role of the phospholipid exchange protein (PLEP) in the lung surfactant system. We propose to assay for PLEP activity in the neonatal lamb lung, to purify and characterize this protein and to determine the specificity with regard to the transfer of saturated vs. unsaturated phosphatidylcholine to subcellular organelles such as the osmiophilic inclusion bodies thought to be the location of lung surfactant storage. Subsequent to characterization of this system in the newborn we propose to study it in the fetal lamb to determine its relationship to pulmonary maturation. Subsequent studies are planned to investigate the role of this system in the respiratory distress syndrome using the asphyxiated fetal lamb model. These experiments should provide additional information pertinent to the understanding of the lung surfactant system in the adult and in the developing and asphyxiated fetus.